Foot fencing is a colloquial term -- usually used in a derogatory fashion -- to describe a style of taekwondo sparring in which the athletes each keep one leg in the air, each athlete hopping around the other on one foot, in an attempt to score a kick with the lofted leg. In other words, the athletes are "fencing" using legs instead of swords. In many sport-style tournaments this style of sparring is technical legal, but is considered "bad form" -- i.e., it's not really taekwondo, even though it's not breaking any rules. This style became increasingly common after adoption of electronic hogus, as the sensors could detect a slight poke of the leg and register it as a hit, while a human judge would likely not score the hit due to clear lack of power. Some tournaments now impose rules about how long one leg may be lofted in the air at a single time, usually limiting this to something on the order of 3 seconds.